The present invention relates to a die clamping apparatus, a die clamping method, and a method for adjustment to die thickness using the die clamping apparatus, which are used for an injection molding machine or the like.
Conventionally, there is available a die clamping apparatus for an injection molding machine, which includes a fixed die plate for holding a fixed die, a moving die plate for holding a moving die, displacing means for advancing and retreating the moving die plate with respect to the fixed die plate, and die clamping means for coupling and pressing the moving die plate to the fixed die plate via a tie bar.
In the die clamping apparatus of this type, when a molten material is injected, a high die clamping force is required in order to restrain the opening of die due to the pressure in the die, and on the other hand, when a product is taken out, it is required to open the die by moving it rapidly through a necessary distance.
Therefore, the conventional die clamping apparatus is configured so that the moving die plate is advanced or retreated with respect to the fixed die plate by using a hydraulic cylinder with a small diameter and a long stroke, whereby the die can be moved rapidly when a product is taken out.
Also, conventionally, there has been used a system in which a die clamping cylinder with a large diameter and a short stroke is provided to derive a high die clamping force during the die clamping operation, and an oil pressure is applied to a large-diameter ram in the die clamping cylinder, whereby the moving die plate is coupled and pressed to the fixed die plate via the tie bar with a high die clamping force.
In the die clamping apparatus as described above, when the die is replaced by another die with a different thickness, the position of the moving die plate at the time of die closure and opening changes, and accordingly the connecting position of the moving die plate and the tie bar also changes. Therefore, each time the die is replaced, it is necessary to change the position of the moving die plate to adjust the connecting position of the moving die plate and the tie bar.
Thereupon, various methods for adjustment to die thickness have been proposed in which the connecting position of the moving die plate and the tie bar can be adjusted in response to the replacement of die by a die with a different thickness.
Hereunder, as an example of the adjusting method, the case of a die clamping apparatus described in Japanese Patent Provisional Publication No. 8-276482 (No. 276482/1996) will be explained.
FIG. 4 shows a die clamping apparatus for an injection molding machine described in the aforementioned Publication and, more particularly, a typical die clamping apparatus provided with a device for adjusting the position of a moving die plate.
This die clamping apparatus has means for coupling and pressing a moving die plate 9 to a fixed die plate 5 via a plurality of tie bars 15. This coupling/pressing means includes die clamping cylinders 11 incorporated in the fixed die plate 5, the tie bars 15 each of which is connected directly to a ram 13 in the die clamping cylinder 11 and has ring grooves 15a at the distal end portion thereof, and half nuts 29 installed on the moving die plate 9. The half nuts 29 can position the moving die plate 9 by being engaged with the ring grooves 15a in the tie bar 15.
Further, this die clamping apparatus includes driving means (an auxiliary cylinder 47, a piston 49) for advancing and retreating the ram 13 when each of the die clamping cylinders 11 is not under pressure (under atmospheric pressure), tie bar position detecting means (a position sensor 55, a scale 57) for detecting an individual position in the movement direction of each of the tie bars 15, and moving die plate position detecting means (a position sensor 41, a scale 43) for detecting a position in the movement direction of the moving die plate 9. The relative position of the half nuts 29 and the tie bar 15 is calculated individually based on the detection signal sent form these detecting means, and thus the aforementioned driving means (not shown) is controlled so that the half nuts 29 are engaged with the ring grooves 15a in the tie bar 15. This control unit uses ordinary means, and therefore the description thereof is omitted.
In the device for adjustment to die thickness in the conventional die clamping apparatus, as shown in FIG. 4, since many construction parts are installed on the outside of the fixed tie plate 5, the manufacturing cost is high. Also, before the pressure is increased to clamp the die, it is necessary to move the tie bars 15 to the right in FIG. 4 in advance by sending a pressure oil into the die clamping cylinder 11 in order to eliminate a gap between the ring grooves 15a in the die bar 15 and the ring grooves in the half nuts 29. However, the die clamping cylinder 11 of the die clamping apparatus is generally formed so as to have a large diameter because it must provide a high clamping force, so that it is necessary to supply a large quantity of pressure oil to operate the die clamping cylinder 11. Therefore, there arises a problem in that useless time is produced during the time from when the pressure oil is poured to when the tie bar moves.
Accordingly, an object of the present invention is to provide a die clamping apparatus in which the number of construction parts is small, so that the apparatus can be manufactured at a low cost, and also to provide a die clamping apparatus, a die clamping method, and a method for adjustment to die thickness using the apparatus, in which useless time for eliminating a gap between the ring grooves in the tie bar and the engagement teeth of the half nuts can be reduced a loss of time in the adjustment to die thickness necessary when the die is replaced.
To achieve the above object, the present invention provides a die clamping apparatus comprising a fixed die plate for holding a fixed die; a moving die plate for holding a moving die; displacing means for advancing and retreating the moving die plate with respect to the fixed die plate; and die clamping means, which is incorporated in either one of the fixed die plate and the moving die plate, for coupling and pressing the moving die plate to the fixed die plate via a tie bar, wherein the die clamping means is provided with a die clamping cylinder consisting of two stages of a large-diameter cylinder and a small-diameter cylinder, and a ram formed into two stages of a large-diameter ram and a small-diameter ram; the large-diameter ram is inserted in the large-diameter cylinder, and the small-diameter ram is inserted in the small-diameter cylinder; the proximal end portion of the tie bar is connected directly to the small-diameter ram; a large oil chamber is provided on each side of the large-diameter ram, and a small oil chamber is provided on the tie bar connection side of the small-diameter ram; and oil pressure supply means is provided which appropriately supplies an oil pressure to the large oil chamber and the small oil chamber in the die clamping cylinder to appropriately move the tie bar.
Also, the present invention provides a die clamping method in which using the above-described die clamping apparatus, a pressure oil is supplied to the small oil chamber to move the tie bar, and after an engagement gap between the half nuts and the tie bar is eliminated, a pressure oil is supplied to the small oil chamber and the large oil chamber on the small ram side to create a die clamping force.
Further, the present invention provides a method for adjustment to die thickness, in which when adjustment to die thickness is made using the above-described die clamping apparatus, the ram is located at a position of limit end to which the ram can be moved, and after the pressures in the large oil chambers on both sides of the large-diameter ram are decreased, a pressure oil is supplied to the small oil chamber to move the ram in the die clamping direction, by which the tie bar is located at a position at which the ring grooves in the tie bar engage properly with the ring grooves in the half nuts.